Thunderstorms are a major weather hazard, but are difficult to predict. They can travel at speeds of 20 km/h to 40 km/h, and lightning strokes may occur more than 10 km in front of the rain clouds and equally some distance behind the rain clouds. While a lightning stroke is produced by a cloud or a weather front, many of the most dangerous lightning strokes actually occur when no visible clouds are present above as a warning of a thunderstorm. Thus, a system that warns of possibility harmful thunderstorms, even if only approximately ten minutes before they become visible, can be considered a major safety feature.
There is a large population that would benefit from such a safety feature. To some persons, it might provide only a nice-to-know everyday knowledge. To a considerable number of persons, however, storm and lightning originated threats have significant implications in the form of an increased risk, loss of property or even fatal consequences. A lightning alerting system is of particular interest, for instance, for persons spending much time outdoors, and equally for aviators, navigators or the like. A system providing a warning of lightning even when the weather seems to be perfectly calm and clear may enable a person to take suitable safety measures in time, for instance to seek shelter etc.
From the state of the art, many single-purpose lightning detectors are known, but they have some disadvantages from a commercial perspective. Scientific lightning detectors, which are used in meteorology, are very large and their range is hundreds of kilometers.
Also other high-end lightning detectors using a single radio frequency (RF) band are large and relatively expensive, compared for instance to mobile phones. Moreover, they are usually required to have a specific orientation, for instance standing on a wall or on a desk stand, in order to gain the required accuracy or directionality. They are thus not well suited for a truly mobile use. These devices typically have further to be vertically positioned and held stable for several minutes before a reliable detection of a thunderstorm becomes possible.
In addition, there are now existing rather inexpensive lowend lightning detectors which are completely portable in size and which do not require a specific orientation. These detectors, however, are extremely susceptible to electromagnetic compatibility (EMC) emissions and thus tend to cause spurious alarms especially in an urban setting or near highways.
Currently most of commercially available mobile lightning detectors detect lightning strokes by measuring the electromagnetic emission caused by lightning at very low frequencies (VLF: 3 to 30 kHz). In addition, it has been known for decades that lightning strokes can be “heard” by using a traditional AM broadcast radio receiver, which operates at longwave frequencies (150 to 300 kHz) and medium wave frequencies (500 to 1700 kHz). However, numerous publications exist where lightning have been detected and measured by its emission at HF and VHF frequencies between 3-300 MHz and even at higher (UHF) frequencies.